JP2024018352A - Optically clear adhesive sheet - Google Patents

Abstract

To provide an optically clear adhesive sheet which does not require photocuring and is excellent in flexibility and thermal stability.SOLUTION: The optically clear adhesive sheet includes a polyurethane layer comprising a cured product of a thermosetting polyurethane composition. The thermosetting polyurethane composition contains a polyol having an olefin skeleton as a polyol component and contains a first polyisocyanate having a functional group number of isocyanate groups of 3 or more and a second polyisocyanate being an aliphatic and/or alicyclic polyisocyanate, as a polyisocyanate component.SELECTED DRAWING: Figure 1

Description

The following disclosure relates to an optically transparent adhesive sheet.

An optically clear adhesive (OCA) sheet is a transparent adhesive sheet used for bonding optical members together. In recent years, demand for touch panels has been rapidly increasing in fields such as smartphones, tablet PCs, portable game machines, and car navigation devices, and with this, demand for OCA sheets used to bond touch panels to other optical components has increased. is also increasing. A display device equipped with a touch panel usually includes a display panel such as a liquid crystal panel, a transparent member (touch panel body) having a transparent conductive film made of ITO (indium tin oxide) or the like on its surface, and a cover that protects the transparent conductive film. It has a structure in which optical members such as panels are laminated, and an OCA sheet is used to bond the optical members together.

For bonding optical members, for example, a photosensitive resin composition containing a (meth)acrylate compound (e.g., Patent Document 1), a two-component thermosetting polyurethane resin composition (e.g., Patent Document 2), etc. are used. This is also being considered.

Patent Document 1 discloses a polyurethane compound (F) that is a reaction product of compound (A), compound (B), compound (C), compound (D), and compound (E) shown below.
Compound (A): Hydrogenated polybutadiene polyol compound Compound (B): Polyisocyanate compound having three or more functional isocyanate groups Compound (C): Diisocyanate compound Compound (D): Polyol compound other than compound (A) Compound (E) ): (meth)acrylate compound having at least one hydroxyl group

Patent Document 2 discloses that the polyol (A) contains a hydrogenated dimer diol (a-1) and a hydroxyl-terminated hydrogenated polybutadiene (a-2), and a polyisocyanate (B), and the polyol (A) contains a polyisocyanate (B). ), the mass ratio of hydrogenated dimer diol (a-1) and hydroxyl group-terminated hydrogenated polybutadiene (a-2) is hydrogenated dimer diol (a-1)/hydroxyl group-terminated hydrogenated polybutadiene (a-2). Disclosed is a two-component thermosetting polyurethane resin composition characterized in that the ratio is 99.5/0.5 to 80/20.

Japanese Patent Application Publication No. 2017-057349 JP2013-018856A

For bonding optical members, an OCA sheet is required that has transparency, flexibility to follow the height difference of a bezel, etc., and a thick film that can cover the thickness of a bezel, etc. A photosensitive resin composition containing a (meth)acrylate compound as described in Patent Document 1 is polymerized and cured (photocured) by irradiation with light such as ultraviolet rays when bonding optical members together, so that a thick film is formed. It was difficult to fully cure the OCA sheet to the center. Furthermore, there was room for further study regarding the stability of the OCA sheet.

The present invention was made in view of the above-mentioned current situation, and an object of the present invention is to provide an optically transparent pressure-sensitive adhesive sheet that does not require photocuring and has excellent flexibility and thermal stability.

(1) One embodiment of the present invention is an optically transparent adhesive sheet including a polyurethane layer made of a cured product of a thermosetting polyurethane composition, wherein the thermosetting polyurethane composition contains an olefin skeleton as a polyol component. an optically transparent polyisocyanate containing, as a polyisocyanate component, a first polyisocyanate in which the number of functional groups in the isocyanate group is 3 or more, and a second polyisocyanate that is an aliphatic and/or alicyclic polyisocyanate. adhesive sheet.

(2) Furthermore, an embodiment of the present invention is an optically transparent pressure-sensitive adhesive sheet, in which, in addition to the configuration described in (1) above, the first polyisocyanate is an aliphatic polyisocyanate containing three or more isocyanate groups.

(3) Furthermore, an embodiment of the present invention is an optically transparent pressure-sensitive adhesive sheet, in which, in addition to the above configuration (1) or (2), the polyisocyanate component further contains a modified polyisocyanate containing an alkylene oxide unit.

(4) Further, in an embodiment of the present invention, in addition to any one of the configurations (1) to (3) above, the polyol having an olefin skeleton has an optically transparent pressure-sensitive adhesive sheet in which the number of functional groups of hydroxyl groups is less than 2. .

(5) Furthermore, an embodiment of the present invention provides an optically transparent pressure-sensitive adhesive sheet, in addition to any one of the configurations (1) to (4) above, wherein the thickness of the polyurethane layer is 200 μm or more and 2000 μm or less.

(6) In addition to any of the configurations (1) to (5) above, an embodiment of the present invention includes the polyurethane layer and a first surface adhesive disposed on one surface of the polyurethane layer. An optically transparent pressure-sensitive adhesive sheet comprising: an adhesive layer; and a second surface adhesive layer disposed on the other side of the polyurethane layer.

According to the present invention, it is possible to obtain an optically transparent pressure-sensitive adhesive sheet that does not require photocuring and has excellent flexibility and thermal stability.

FIG. 1 is a schematic cross-sectional view showing an example of an optically transparent adhesive sheet according to an embodiment. FIG. 3 is a schematic cross-sectional view showing another example of the optically transparent pressure-sensitive adhesive sheet according to the embodiment. 3 is a graph showing the curing time of optically transparent adhesive sheets according to Examples 7 to 10.

The optically transparent adhesive sheet according to the embodiment is an optically transparent adhesive sheet including a polyurethane layer made of a cured product of a thermosetting polyurethane composition, wherein the thermosetting polyurethane composition has an olefin skeleton as a polyol component. The polyisocyanate component contains a first polyisocyanate whose isocyanate group has a functional number of 3 or more, and a second polyisocyanate which is an aliphatic and/or alicyclic polyisocyanate.

An optically transparent adhesive sheet (hereinafter referred to as an OCA sheet) includes a polyurethane layer made of a cured product of a thermosetting polyurethane composition. Since the thermosetting polyurethane composition can be formed into a film without using a solvent, the resulting polyurethane layer can be thickened. In addition, unlike photosensitive resin compositions containing (meth)acrylate compounds, the composition does not require ultraviolet irradiation during curing, and is therefore suitable for thickening films. The OCA sheet according to the embodiment stretches well when tensile stress is applied and is extremely difficult to tear. Therefore, it can be peeled off without leaving any adhesive residue. Furthermore, since the polyurethane layer has a high dielectric constant, the OCA sheet according to the embodiment has a higher capacitance than an OCA sheet made of a conventional acrylic resin composition, and is suitable for bonding capacitive touch panels. It is suitably used for.

The polyurethane layer is obtained by reacting a polyol component and a polyisocyanate component, and preferably has, for example, the structure shown in chemical formula (A).

In the chemical formula (A), R represents the site of the polyisocyanate component excluding the NCO group, R' represents the site of the polyol component excluding the OH group, and n represents the number of repeating units.

The cured product of the thermosetting polyurethane composition (thermosetting polyurethane) is preferably not acrylic modified, and preferably does not contain a moiety derived from acrylic ester, methacrylic ester, etc. in the main chain of the polyurethane. . When thermosetting polyurethane is acrylic-modified, it becomes hydrophobic, so water tends to aggregate under high temperature and high humidity conditions. This aggregation of water causes whitening, foaming, etc., and may impair optical properties. Furthermore, if it is acrylic modified, it may turn yellow due to high temperatures. Therefore, by using thermosetting polyurethane that is not acrylic-modified, it is possible to prevent deterioration of optical properties and yellowing under high temperature and high humidity conditions.

In the polyurethane layer made of the cured product of the thermosetting polyurethane composition, the total amount of monomer units derived from the polyol component and monomer units derived from the polyisocyanate component constitutes the entire thermosetting polyurethane. It is preferably 80 mol% or more, more preferably 90 mol% or more of the monomer units.

As the polyol component and the polyisocyanate component, those that are both liquid at room temperature (23° C.) can be used, and a thermosetting polyurethane can be obtained without using a solvent. Other components such as tackifiers can be added to either the polyol component or the polyisocyanate component, and are preferably added to the polyol component. Since thermosetting polyurethane does not require removal of solvent, it is possible to form a uniform thick sheet, and it is possible to produce a flexible and thick polyurethane layer. Further, even if the polyurethane layer is formed thick, optical characteristics can be maintained.

[Polyol component]
The thermosetting polyurethane composition contains a polyol having an olefin skeleton as a polyol component. By containing a polyol having an olefin skeleton, it is possible to obtain a polyurethane layer with excellent thermal stability compared to the case where an acrylic, ester, or polyether polyol is used. For example, a polyurethane layer that does not dissolve or yellow even when left at 95° C. for 1000 hours can be obtained.

The main chain of the polyol having an olefin skeleton is composed of a polyolefin or a derivative thereof. Examples of the polyols having an olefin skeleton include polybutadiene polyols such as 1,2-polybutadiene polyol, 1,4-polybutadiene polyol, 1,2-polychloroprene polyol, and 1,4-polychloroprene polyol, and polyisoprene-based polyols. Examples thereof include polyols and polyols whose double bonds are saturated with hydrogen or halogen. Further, the polyol component may be a polyol obtained by copolymerizing a polybutadiene polyol or the like with an olefin compound such as styrene, ethylene, vinyl acetate, or acrylic ester, or a hydrogenated product thereof. The polyol component may have a linear structure or a branched structure. Only one type of the above-mentioned polyol component may be used, or two or more types may be used.

The polyol component used in the thermosetting polyurethane composition preferably contains 80 mol% or more of a polyol having an olefin skeleton, and more preferably consists only of a polyol having an olefin skeleton.

Examples of the above-mentioned polybutadiene polyols include Claysol (registered trademark) HLBHP3000 and Claysol HLBHP2000 manufactured by Tomoe Kogyo, and GI1000, GI2000, and GI3000 manufactured by Nippon Soda Co., Ltd. Examples of the polyisoprene polyol include Epol (registered trademark) manufactured by Idemitsu Kosan Co., Ltd., and the like.

The polyol having an olefin skeleton may have a structure shown in chemical formula (B).

In chemical formula (B), x, y and z represent the number of repeating units. In the polybutadiene polyol, X in the chemical formula (B) is a hydrogen group, and in the polyisoprene polyol, X in the chemical formula (B) is a methyl group.

It is preferable that the polyol having an olefin skeleton has a functional number of hydroxyl groups of less than 2. The number of functional groups of hydroxyl groups mentioned above is the average number of functional groups of hydroxyl groups per mole of polyol having an olefin skeleton. If the number of functional groups in the hydroxyl group is less than 2, it is difficult to form a branched structure when curing the thermosetting polyurethane composition, so the polyurethane layer may become too soft or the curing speed may be slow. In particular, when a polyisocyanate having 3 or more functional groups is used for a polyol component having hydroxyl functional groups of less than 2, the viscoelasticity can be adjusted while increasing the curing speed.

The number of hydroxyl functional groups in the entire polyol component is preferably less than two. If multiple types of polyol components are included and the blending ratio of each polyol component and the number of hydroxyl functional groups in each polyol component are known, the number of hydroxyl functional groups in the entire polyol component is determined by the blending ratio of each polyol component and the number of hydroxyl groups. It can be calculated from the number of functional groups. In addition, by gel permeation chromatography (GPC), the blending ratio of each polyol component contained in the entire polyol component is calculated from the peak area corresponding to each polyol component, and separately, the number of functional groups of hydroxyl groups in the entire polyol component is determined by titration. It is also possible to calculate the number of functional groups of hydroxyl groups in the entire polyol component.

[Polyisocyanate component]
The thermosetting polyurethane composition contains, as a polyisocyanate component, a first polyisocyanate in which the number of functional groups in the isocyanate group is 3 or more, and a second polyisocyanate that is an aliphatic and/or alicyclic polyisocyanate. do. By using the first polyisocyanate, it is possible to form many branched structures when curing the thermosetting polyurethane composition and increase the rigidity of the polyurethane layer, so it is possible to reduce the amount of polyisocyanate component added. Also, the desired viscoelasticity can be obtained. Furthermore, since many of the above-mentioned branched structures can be formed, the polyurethane growth reaction can be favorably promoted and the curing speed of the polyurethane layer can be increased.

The first polyisocyanate is a polyisocyanate in which the number of functional groups in the isocyanate group is 3 or more (hereinafter also referred to as polyisocyanate with 3 or more functional groups). The number of functional groups in the isocyanate group is the average number of functional groups in the isocyanate group per mole of the first polyisocyanate. The number of functional groups of the isocyanate groups of the first polyisocyanate component may be, for example, 4.0 or less.

The first polyisocyanate is preferably an aliphatic polyisocyanate containing three or more isocyanate groups. The aliphatic polyisocyanate containing three or more isocyanate groups may be synthesized using an aliphatic polyisocyanate described later as a second polyisocyanate. Specific examples of aliphatic polyisocyanates containing three or more isocyanate groups include Desmodur N3900 (number of functional groups in isocyanate groups = 3.2) and Desmodur N3600 (number of functional groups in isocyanate groups = 3.2) manufactured by Covestro. , Desmodur N3300 (number of functional groups in isocyanate groups = 3.5), Desmodur N3800 (number of functional groups in isocyanate groups = 3.2), and the like.

The second polyisocyanate is an aliphatic and/or alicyclic polyisocyanate. Specific examples of the aliphatic polyisocyanate include hexamethylene diisocyanate (HDI), tetramethylene diisocyanate, 2-methyl-pentane-1,5-diisocyanate, 3-methyl-pentane-1,5-diisocyanate, and lysine diisocyanate. , trioxyethylene diisocyanate, modified products thereof, and the like. Specific examples of the alicyclic polyisocyanate include isophorone diisocyanate (IPDI), cyclohexyl diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, norbornane diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated xylene diisocyanate, and hydrogenated tetramethyl. Examples include xylene diisocyanate and modified products thereof. These may be used alone or in combination of two or more.

Among these, hexamethylene diisocyanate, isophorone diisocyanate, and modified products thereof are preferred, and isophorone diisocyanate and modified products thereof are particularly preferred. Examples of modified isophorone diisocyanate include isophorone diisocyanate modified with isocyanurate, allophanate, and/or urethane. Specific examples of IPDI (isophorone diisocyanate) polyisocyanates include Desmodur I and Desmodur H manufactured by Covestro.

It is preferable that the polyisocyanate component further contains a modified polyisocyanate (third polyisocyanate) containing an alkylene oxide unit. Modified polyisocyanate containing an alkylene oxide unit can suppress whitening due to moisture absorption by the action of the hydrophilic part (polyalkylene oxide unit), and can suppress whitening due to moisture absorption by the action of the hydrophobic part (other units). It can exhibit compatibility with plasticizers and the like. Since the third polyisocyanate is a hydrophilic polyisocyanate, by using it together with the second polyisocyanate, which is a hydrophobic polyisocyanate, it adjusts the balance between hydrophilicity and hydrophobicity of the polyurethane layer and provides long-term durability. This makes it possible to maintain the transparency of the OCA sheet while suppressing whitening due to moisture absorption.

The above-mentioned modified polyisocyanate containing an alkylene oxide unit may be obtained by reacting the above-mentioned aliphatic and/or alicyclic polyisocyanate with an ether compound having a polyalkylene oxide unit. Examples of the alkylene oxide unit include ethylene oxide unit and propylene oxide unit. Specific examples of modified polyisocyanates containing ethylene oxide units include HC266, Coronate 4021, Aquanate 130, and Aquanate 140 manufactured by Tosoh Corporation.

The mass ratio of the second polyisocyanate to the third polyisocyanate is preferably 2:1 to 1:2. By setting the mass ratio within the above range, the compatibility between the polyisocyanate component and the polyol component and the hygroscopicity of the polyurethane layer can be adjusted. A more preferable range of the above mass ratio is 1:1 to 1:1.5.

The content of the first polyisocyanate based on the entire polyisocyanate component is preferably 2% by mass or more and 10% by mass or less. By setting the content of the first polyisocyanate within the above range, viscoelasticity such as loss tangent can be adjusted, and flexibility of the polyurethane layer can be adjusted while maintaining transparency. From the viewpoint of further suppressing whitening of the polyurethane layer, the content of the first polyisocyanate is more preferably 5% by mass or less.

The number of functional groups of isocyanate groups in the entire polyisocyanate component is preferably 2 or more. The number of functional groups of isocyanate groups in the entire polyisocyanate component may be, for example, 4 or less. If multiple types of polyisocyanate components are included and the blending ratio of each polyisocyanate component and the number of functional groups of isocyanate groups of each polyisocyanate component are known, the number of functional groups of isocyanate groups of the entire polyisocyanate component is determined by the number of functional groups of isocyanate groups of each polyisocyanate component. It can be calculated from the blending ratio of isocyanate components and the number of functional groups of isocyanate groups. Further, by gel permeation chromatography (GPC), the component ratio of each polymer contained in the polyisocyanate component can be calculated, and the number of functional groups in the polyisocyanate component can be calculated.

The thermosetting polyurethane composition preferably has an α ratio (number of moles of OH groups derived from the polyol component/number of moles of NCO groups derived from the polyisocyanate component) of 1.00 or more. If the α ratio is less than 1.00, the amount of polyisocyanate component blended is excessive with respect to the amount of polyol component blended, so the thermosetting polyurethane becomes hard and the flexibility of the OCA sheet may decrease. be. The α ratio is more preferably 1.00 to 2.00. If the α ratio exceeds 2.00, the thermosetting polyurethane composition may not be sufficiently cured. The α ratio is more preferably 1.00 or more and 1.40 or less. From the viewpoint of increasing the curing speed of the polyurethane layer, the α ratio is more preferably 1.20 or more and 1.35 or less.

[Tackifier]
The thermosetting polyurethane composition may further contain a tackifier. Examples of the tackifier include petroleum resin-based, hydrocarbon resin-based, rosin-based, and terpene-based tackifiers. Petroleum resin-based tackifiers are preferably used because they have excellent compatibility with polyols and the like having the above-mentioned olefin skeletons. Among the above petroleum resin tackifiers, hydrogenated petroleum resins obtained by hydrogenating a copolymer of dicyclopentadiene and an aromatic compound are preferred. A known example of the above hydrogenated petroleum resins is "Imarv P-100" manufactured by Idemitsu Kosan Co., Ltd.

The content of the tackifier is preferably 5 parts by weight or more and 25 parts by weight or less based on 100 parts by weight of the polyol component. If the content of the tackifier is less than 5 parts by weight, the polyol component and the polyisocyanate may be difficult to mix. If the content of the tackifier exceeds 25 parts by weight, the haze of the polyurethane layer may become low.

[catalyst]
The thermosetting polyurethane composition may further contain a catalyst. The catalyst is not particularly limited as long as it is a catalyst used in the urethanization reaction, and examples thereof include organic tin compounds such as di-n-butyltin dilaurate, dimethyltin dilaurate, dibutyltin oxide, and octanetin; organic titanium compounds. ; organic zirconium compounds; tin carboxylate salts; bismuth carboxylate salts; and amine catalysts such as triethylenediamine.

The content of the catalyst may be 50 ppm or more and 200 ppm or less based on 100 parts by weight of the polyol component.

[Light stabilizer]
The thermosetting polyurethane composition may further contain a light stabilizer. As the light stabilizer, a hindered amine light stabilizer can be suitably used.

When the OCA sheet is exposed to an ultraviolet irradiation environment, for example under metal halide lamp irradiation, the polyurethane layer may dissolve. The dissolution of the polyurethane layer is thought to be caused by the reaction between photoactivated oxygen molecules, hydroxyl radicals, etc. and the ether bond portion of the polyurethane. Furthermore, in a high-temperature environment, the above-mentioned radicals and the like are likely to be generated, so that the polyurethane layer tends to be easily dissolved. Since the hindered amine light stabilizer can capture the above-mentioned radicals, it can suppress dissolution of the polyurethane layer even if the OCA sheet is left in an environment of high temperature and ultraviolet irradiation.

The hindered amine light stabilizer is not particularly limited, and examples include bis-(2,2,6,6-tetramethyl-4-piperidyl) sebacate, [dimethyl-1-(2-hydroxyethyl)-4 succinate] -hydroxy-2,2,6,6-tetramethylpiperidine] condensate, 1,2,2,6,6-pentamethyl-4-piperidyl-tridecyl-1,2,3,4-butanetetracarboxylate, 1 , 2,2,6,6-pentamethyl-4-piperidinol, 3,9-bis(2-hydroxy-1,1-dimethylethyl)-2,4,8,10-tetraspiro[5,5]undecane and butane Examples include esters with tetracarboxylic acids. These may be used alone or in combination of two or more.

Specific examples of the hindered amine light stabilizer include ADEKA STAB LA-81, ADEKA STAB LA-63P, ADEKA STAB LA-72, and the like.

ADK STAB LA-81 contains a compound represented by the following chemical formula (1).

ADK STAB LA-63P contains a compound represented by the following chemical formula (2).

（式（２）中、ｎは自然数である。）

(In formula (2), n is a natural number.)

ADK STAB LA-72 contains a compound represented by the following chemical formula (3).

The content of the hindered amine light stabilizer may be 0.1 part by weight or more and 1 part by weight or less based on 100 parts by weight of the polyol component. If the content of the hindered amine light stabilizer exceeds 1 part by weight, the light stabilizer may bleed from the polyurethane layer.

The thickness of the polyurethane layer is preferably 200 μm or more and 2000 μm or less. A more preferable lower limit of the thickness of the polyurethane layer is 300 μm. The polyurethane layer is a cured product of a thermosetting polyurethane composition, and can be formed without using a solvent, so it can be made thicker while maintaining optical properties.

The loss tangent (tan δ _85°C ) of the polyurethane layer at 85°C is preferably 0.10 or more and less than 0.50. By setting it as the above range, the polyurethane layer can obtain excellent flexibility. When the tan δ _{85° C.} of the polyurethane layer is less than 0.50, deformation at high temperatures can be more effectively suppressed. Further, from the viewpoint of effectively suppressing delay bubbles under high temperature and high humidity conditions (85° C., 85%), it is more preferable that the tan δ _{85° C.} is 0.17 or more. The tan δ of _{85° C.} of the polyurethane layer can be adjusted by changing the α ratio of the thermosetting polyurethane composition, the structure and number of functional groups of the polyisocyanate component, and the structure and number of functional groups of the main ingredient of the polyol component.

The loss tangent is expressed as the ratio (G''/G') of the storage modulus (G') and the loss modulus (G''). The loss tangent can be measured using, for example, a viscoelasticity measuring device "Physica MCR301" manufactured by Anton Paar Germany GmbH.

The optically transparent adhesive sheet only needs to include at least a polyurethane layer made of a cured product of a thermosetting polyurethane composition, and may include other layers. FIG. 1 is a schematic cross-sectional view showing an example of an optically transparent adhesive sheet according to an embodiment. FIG. 2 is a schematic cross-sectional view showing another example of the optically transparent adhesive sheet according to the embodiment. As shown in FIG. 1, the OCA sheet 10 may consist only of a polyurethane layer 11. Further, as shown in FIG. 2, the OCA sheet 10 includes a polyurethane layer 11, a first surface adhesive layer 12 disposed on one surface of the polyurethane layer 11, and a first surface adhesive layer 12 disposed on the other surface of the polyurethane layer 11. It may also include a second surface adhesive layer 13 arranged thereon.

The first surface adhesive layer 12 and the second surface adhesive layer 13 may each be located on the outermost surface of the OCA sheet 10 (the surface in contact with the adherend). Although other layers may be provided between the first surface adhesive layer 12 and the polyurethane layer 11 and between the second surface adhesive layer 13 and the polyurethane layer 11, the first surface It is preferable that the adhesive layer 12 and the polyurethane layer 11 are in contact with each other, and that the second surface adhesive layer 13 and the polyurethane layer 11 are in contact with each other.

The first and second surface adhesive layers may contain polyurethane. The above-mentioned polyurethane is a cured product of a polyurethane composition, and the same polyurethane composition as the thermosetting polyurethane composition used for the above-mentioned polyurethane layer can be used.

The first and second surface adhesive layers may contain an acrylic resin. By placing a surface adhesive layer containing acrylic resin on the surface of the polyurethane layer, the polyurethane layer provides flexibility, while the surface adhesive layer containing acrylic resin improves adhesion to the adherend. can be done. The surface adhesive layer containing an acrylic resin can be produced by curing an acrylic resin composition.

The acrylic resin composition includes, for example, a (meth)acrylic acid ester polymer or a copolymer thereof (hereinafter also referred to as a (meth)acrylic copolymer) and a crosslinking agent. There are many things that can be mentioned. Examples of the (meth)acrylic copolymer include a copolymer of a (meth)acrylic acid alkyl ester and a carboxyl group-containing monomer.

The (meth)acrylic acid alkyl ester mentioned above is a (meth)acrylic acid alkyl ester in which the alkyl group has 1 to 18 carbon atoms (CH ₂ =CR ¹ -COOR ² ; R ¹ is a hydrogen atom or a methyl group, and R ² is an alkyl group having 1 to 18 carbon atoms), and the alkyl group preferably has 4 to 12 carbon atoms.

Examples of the (meth)acrylic acid alkyl esters in which the alkyl group has 1 to 18 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate , isooctyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undeca (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate Can be mentioned. These may be used alone or in combination of two or more.

Examples of the carboxyl group-containing monomer include β-carboxyethyl (meth)acrylate, 5-carboxypentyl (meth)acrylate, mono(meth)acryloyloxyethyl succinate, and ω-carboxypolycaprolactone mono(meth) Carboxyl group-containing (meth)acrylates such as acrylates; examples include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid, and maleic acid. These may be used alone or in combination of two or more.

The crosslinking agent is not particularly limited as long as it is a component that can cause a crosslinking reaction with the crosslinkable functional group derived from the crosslinkable functional group-containing monomer possessed by the (meth)acrylic copolymer, for example, isocyanate. compounds, metal chelate compounds, epoxy compounds, etc.

The thickness of the first and second surface adhesive layers is preferably 3 μm or more and 100 μm or less. If the thickness is less than 3 μm, delay bubbles generated from the polyurethane layer may not be sufficiently suppressed. On the other hand, if the thickness exceeds 100 μm, the flexibility of the OCA sheet may decrease. The thickness of the first and second surface adhesive layers is more preferably 3 μm or more and 50 μm or less.

The loss tangent (tan δ _{85° C.} ) of the first and second surface adhesive layers at 85° C. may be equal to or lower than the tan δ _{85° C.} of the polyurethane layer. The tan δ _{85° C.} of the first and second surface adhesive layers may be, for example, 0.10 or more and less than 0.50.

It is preferable that the OCA sheet has a haze of 1% or less. Further, it is preferable that the total light transmittance is 90% or more. Haze and total light transmittance can be measured using, for example, a turbidity meter "HazeMeter NDH2000" manufactured by Nippon Denshoku Industries. Haze is measured according to JIS K 7136, and total light transmittance is measured according to JIS K 7361-1.

It is preferable that the OCA sheet has no coloration (yellowing), and in the L*a*b* color system, for the measured hue, a* is ±0.5 or less, b* is ±0.5 or less, and YI is preferably 1.0 or less. L* is preferably 94% or more, more preferably 96% or more. The above hue can be measured by a method based on JIS Z 8781-4 using "Spectrophotometer CM-3600A" manufactured by Konica Minolta.

The thickness of the entire OCA sheet is preferably 200 μm or more. Although the upper limit of the thickness of the entire OCA sheet is not particularly limited, it is, for example, 3000 μm. A more preferable lower limit of the above thickness is 300 μm, and an even more preferable lower limit is 500 μm.

The loss tangent (tan δ _85°C ) of the OCA sheet at 85°C is preferably 0.10 or more and less than 0.50. By setting it as the said range, an OCA sheet can obtain excellent flexibility. When the tan δ _{85° C.} of the OCA sheet is less than 0.50, deformation at high temperatures can be more effectively suppressed. Further, from the viewpoint of effectively suppressing delay bubbles under high temperature and high humidity conditions (85° C., 85%), it is more preferable that the tan δ _{85° C.} is 0.17 or more.

The flexibility of the OCA sheet can be evaluated by measuring the loss tangent (tan δ). The lower the tan δ, the harder the OCA sheet becomes, and the higher the tan δ, the softer the OCA sheet becomes. When the OCA sheet includes a polyurethane layer and a surface adhesive layer, the value of tan δ of the layer with the largest tan δ is measured as the tan δ of the OCA sheet, so the tan δ of the polyurethane layer can be regarded as the tan δ of the OCA sheet. .

The peeling force of the OCA sheet is preferably 15 N/25 mm or more, and more preferably 20 N/25 mm or more. By setting the peeling force of the OCA sheet to 15 N/25 mm or more, delay bubbles can be effectively suppressed. Furthermore, it has excellent adhesive strength even when the OCA sheet is attached substantially perpendicular to the ground. Note that the above peeling force is measured by a method based on JIS K 6854-2. A slide glass was pasted on one surface of the OCA sheet, a PET sheet was pasted on the other surface, and the sheets were crimped by holding at a pressure of 0.4 MPa for 30 minutes in an environment of room temperature (23°C) and 50% humidity. After 1 minute, the OCA sheet was peeled off at the interface between the OCA sheet and the slide glass at a peeling speed of 300 mm/min and a peeling angle of 180°, and the peeling force was measured. As the PET sheet, for example, a 125 μm thick PET sheet (“Melinex (registered trademark) S” manufactured by Teijin DuPont Films), etc. can be used.

The surface adhesion of the OCA sheet at 85° C. is preferably 10 N/Φ12 mm or more, more preferably 15 N or more, and even more preferably 20 N/Φ12 mm or more. The surface adhesive strength can be measured using a viscoelasticity measuring device, and as the measuring device, “Modular Compact Rheometer MCR 302” manufactured by Anton Paar can be used. Place the test piece below the terminal of the measuring device, set the initial load value of the terminal in contact with the test piece to be 1N/Φ12mm, and hold the terminal until the load value reaches 10N/Φ12mm. After lowering the terminal and pressing it against the test piece and holding it for a certain period of time, the terminal is raised and the maximum load value when the test piece and the terminal peel off is measured as the surface adhesion force.

Release films may be attached to both sides of the OCA sheet. That is, it may be a laminate in which an OCA sheet, a first release film covering one side of the OCA sheet, and a second release film covering the other side of the OCA sheet are stacked.

Examples of the first and second release films include PET films. The surfaces of the first and second release films that are in contact with the OCA sheet may each be subjected to easy-peel treatment (mold release treatment) such as silicone treatment.

The OCA sheet can be suitably used for bonding optical members. Examples of the adherend of the OCA sheet include various members constituting a display device, such as a display panel, a touch panel (glass substrate with an ITO transparent conductive film), a cover panel (cover glass), a polarizing plate, and a retardation film. . The OCA sheet according to the embodiment is a pressure-sensitive adhesive sheet, and when used on an adherend, it does not require curing treatment such as heating or light irradiation, and can be bonded to an adherend by applying pressure. be able to.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

<Ingredients used>
The components used in the following Reference Examples, Examples, and Comparative Examples are shown below.
(A) Polyol component Olefin polyol (A-1): "Craysol (registered trademark) HLBHP3000" manufactured by Tomoe Kogyo, number of functional groups of hydroxyl group = 1.9
Olefin polyol (A-2): "EPOL" manufactured by Idemitsu Kosan Co., Ltd., number of functional groups of hydroxyl group = 2.3
Acrylic polyol (A-3): “UH2190” manufactured by Toagosei Co., Ltd.
Ester polyol (A-4): “T2010” manufactured by Kuraray Co., Ltd.
Polyether polyol (A-5): "PTG-L-2000" manufactured by Hodogaya Chemical

Olefin-based polyols are polyols having an olefin skeleton. The olefin polyol (A-1) is a polybutadiene polyol. The olefin polyol (A-2) is a polyisoprene polyol.

(B) Polyisocyanate component Polyisocyanate (B-1): IPDI (isophorone diisocyanate) polyisocyanate ("Desmodur I" manufactured by Covestro), number of functional groups in isocyanate group = 2.0
Polyisocyanate (B-2): modified polyisocyanate containing ethylene oxide unit (“Coronate 4021” manufactured by Tosoh Corporation), number of functional groups in isocyanate group = 2.0
Polyisocyanate (B-3): polyisocyanate with a functional group number of 3 or more ("Desmodur N3900" manufactured by Covestro), functional group number of isocyanate group = 3.2
Polyisocyanate (B-4): HDI-based polyisocyanate (“HDI” manufactured by Tosoh Corporation), number of functional groups in isocyanate group = 2.0

Polyisocyanate (B-3) was used as the first polyisocyanate. The polyisocyanate having three or more functional groups is an aliphatic polyisocyanate containing three or more isocyanate groups. Polyisocyanate (B-1) was used as the second polyisocyanate. The above IPDI polyisocyanate is an alicyclic polyisocyanate and is a hydrophobic polyisocyanate. Polyisocyanate (B-2) was used as the third polyisocyanate. The modified polyisocyanate containing ethylene oxide units is a hydrophilic polyisocyanate, and is obtained by reacting a polyisocyanate starting from hexamethylene diisocyanate with an ether polyol having an average of three or more ethylene oxide units per molecule. It is something that

(C) Tackifier: Hydrogenated petroleum resin (“Imarv P-100” manufactured by Idemitsu Kosan Co., Ltd.)
(D) Catalyst: dimethyltin dilaurate (“Fomrez catalyst UL-28” manufactured by Momentive)
(E) Light stabilizer: hindered amine light stabilizer (“ADEKA STAB LA-81” manufactured by ADEKA)

<Preliminary exam>
OCA sheets according to Reference Examples 1 to 5 were produced by producing polyurethane compositions using different types of polyols. The transmittance and thermal stability of the obtained OCA sheet were confirmed, and the results are shown in Table 1.

(Reference example 1)
As shown in Table 1 below, olefin polyol (A-1), polyisocyanate (B-4) and the above catalyst (D) were added and mixed with stirring using a reciprocating rotary stirrer agitator to obtain a polyurethane composition. I prepared something. In Table 1, the content of catalyst (D) is the content of dimethyltin dilaurate based on 100 parts by weight of the polyol component.

The obtained polyurethane composition was transported while being sandwiched between a pair of release films (PET films whose surfaces were subjected to release treatment), and was cross-linked and cured under the conditions of an oven temperature of 120°C and an oven time of several minutes. I let it happen. Thereafter, a crosslinking reaction (thermal curing) was carried out at 105° C. for 2 hours using a heating device to produce an OCA sheet with a single polyurethane layer provided with a release film on both sides. The thickness of the polyurethane layer was 1000 μm.

(Reference examples 2 to 5)
As shown in Table 1, polyurethane compositions of Reference Examples 2 to 5 were prepared by blending a polyol component, a polyisocyanate component, and a catalyst with different types. Using each of the obtained polyurethane compositions, an OCA sheet having a single polyurethane layer with a thickness of 1000 μm was produced in the same manner as in Reference Example 1.

(optical properties)
For each OCA sheet obtained, haze and total light transmittance were measured as optical properties. Haze and total light transmittance were measured using a turbidity meter "HazeMeter NDH2000" manufactured by Nippon Denshoku Industries. Haze was measured according to JIS K 7136, and total light transmittance was measured according to JIS K 7361-1. The result is ○ if the haze is 1.0% or less and the total light transmittance is 90% or more, and × if the haze is less than 1.0% or the total light transmittance is less than 90%. are summarized in Table 1. Note that the haze and total light transmittance described above were measured at normal temperature and normal humidity (temperature 23° C., humidity 50%).

(thermal stability)
A test piece was prepared by cutting each OCA sheet into a rectangle of 5 cm x 2.5 cm, and after being left for 1000 hours at a measurement temperature of 95°C and a humidity of 60% or less, it was visually confirmed that the four sides and four corners of the test piece were deformed. A case where the polyurethane layer was dissolved and deformation was observed on at least one of the four sides and four corners of the test piece (yellowing) was judged as ○. Note that the measurement temperature was set at 95° C. assuming the actual usage environment of the OCA sheet.

(yellowing)
A test piece was prepared by cutting each OCA sheet into a rectangle of 5 cm x 2.5 cm, and after being left for 1000 hours at a measurement temperature of 95°C and a humidity of 60% or less, the OCA sheet was Hue was evaluated using the L*a*b* color system. As the measuring device, "spectrophotometer CM-3600A" manufactured by Konica Minolta was used. If a* is ±0.5 or less, b* is ±0.5 or less, and YI is 1.0 or less, it is marked as ○ (no yellowing), and any of a*, b*, and YI is outside the above range. The case where this was the case was classified as × (yellowing).

From the results in Table 2, it was confirmed that by using an olefin polyol as the polyol component, an OCA sheet with high transmittance and excellent thermal stability could be obtained.

Next, the following Examples and Comparative Examples were produced using a polyol having an olefin skeleton as a polyol component.

(Example 1)
<Preparation of polyurethane layer>
To 100 parts by weight of the polyol component, the polyisocyanate component shown in Table 3, 15 parts by weight of the above tackifier (C), and 0.1 part by weight of the above light stabilizer (E) were added, and the above catalyst ( D) was added so that the content of dimethyltin dilaurate was 120 ppm, and the mixture was stirred and mixed using a reciprocating rotary stirrer agitator to prepare a thermosetting polyurethane composition.

The obtained polyurethane composition was transported while being sandwiched between a pair of release films (PET films whose surfaces were subjected to release treatment), and was cross-linked and cured under the conditions of an oven temperature of 120°C and an oven time of several minutes. I let it happen. Thereafter, a crosslinking reaction (thermal curing) was carried out at 110° C. for 2 hours using a heating device to produce a polyurethane layer provided with release films on both sides. The thickness and α ratio of the polyurethane layer are shown in Table 3.

<Preparation of first and second surface adhesive layers>
An epoxy curing agent ("E-AX" manufactured by Soken Kagaku Co., Ltd.) was added to an acrylic resin ("BITF-2" manufactured by Toyo Ink Co., Ltd.) in an amount of 1.5% by mass based on the entire acrylic resin composition. ) was added to prepare an acrylic resin composition.

The obtained acrylic resin composition was applied to a release film using a comma coater and dried in a drying oven at 80 to 120°C to produce an acrylic adhesive layer. The thickness of the acrylic adhesive layer was 25 μm.

<Production of laminated OCA sheet>
Two surface adhesive layers with the release film and one polyurethane layer with the release film were prepared. One of the release films was peeled off from the first and second surface adhesive layers with release films, and the release films were laminated on both sides of the peeled polyurethane layer. As a result, an OCA sheet with a release film was produced, in which the release film, the first surface adhesive layer, the polyurethane layer, the second surface adhesive layer, and the release film were laminated in this order.

(Examples 2 to 6)
As shown in Table 3, a polyurethane composition was prepared in the same manner as in Example 1 except that the polyol component and the polyisocyanate component were blended, and heat curing was performed in the same manner as in Example 1 to form a polyurethane layer. was created. For Examples 2 to 6, the first and second surface adhesive layers were prepared in the same manner as in Example 1, and the release film, first surface adhesive layer, polyurethane layer, and second surface adhesive layer were respectively prepared. An OCA sheet with a release film was prepared in which the agent layer and the release film were laminated in this order.

(Comparative Examples 1 and 2)
Comparative Examples 1 and 2 are comparative examples in which a polyisocyanate having three or more functional groups is not added as a polyisocyanate component. A tackifier, a catalyst, and a light stabilizer were added to the polyol component and polyisocyanate component shown in Table 3 in the same manner as in Example 1 to prepare a polyurethane composition. Heat curing was performed. However, in Comparative Examples 1 and 2, the polyurethane compositions were not thermally cured and remained uncured in the crosslinking reaction at 110° C. for 2 hours. Comparative Example 2 was cured by continuing heat curing, but it took 3 days.

Regarding Comparative Example 2 in which the polyurethane layer was cured, the first and second surface adhesive layers were prepared in the same manner as in Example 1, and the release film, first surface adhesive layer, polyurethane layer, and second surface adhesive layer were respectively prepared. An OCA sheet with a release film was prepared in which a surface adhesive layer and a release film were laminated in this order.

Regarding the OCA sheets according to Examples 1 to 6, loss tangent (tan δ _85°C ) at 85°C, haze and total light transmittance as optical properties were measured. The results are shown in Table 3.

(Haze and total light transmittance)
The haze and total light transmittance of each OCA sheet were measured using a turbidity meter "HazeMeter NDH2000" manufactured by Nippon Denshoku Industries. Haze was measured according to JIS K 7136, and total light transmittance was measured according to JIS K 7361-1. The above haze and total light transmittance were measured at normal temperature and normal humidity (temperature 23° C., humidity 50%).

(loss tangent)
The loss tangent (tan δ _{85° C.} ) of each OCA sheet at 85° C. was measured using a viscoelasticity measuring device “Physica MCR301” manufactured by Anton Paar. The measurement plate used was PP12, the measurement conditions were 0.1% strain, 1 Hz frequency, cell temperature 25°C to 100°C (heating rate 3°C/min), and the loss tangent at 85°C was recorded.

As shown in Table 3, all of Examples 1 to 6 using polyisocyanates with three or more functional groups were sufficiently thermally cured, and a haze of 1.0% or less and a total light transmittance of 90% or more were obtained. It was done.

On the other hand, in Comparative Example 1 which did not contain polyisocyanate having three or more functional groups, the polyurethane layer was not cured. In Comparative Example 2, by lowering the α ratio to 1, thermal curing progressed more than in Comparative Example 1, but it was not cured in the crosslinking reaction at 110° C. for 2 hours.

(Examples 7 to 10)
As shown in Table 4, a polyurethane composition was prepared in the same manner as in Example 1 except that the polyol component and the polyisocyanate component were blended, and heat curing was performed in the same manner as in Example 1 to form a polyurethane layer. was created. Thereafter, in the same manner as in Example 1, first and second surface adhesive layers were prepared, and a release film, a first surface adhesive layer, a polyurethane layer, a second surface adhesive layer, and a release film were prepared, respectively. An OCA sheet with a release film was prepared in which films were laminated in this order.

For the OCA sheets according to Examples 7 to 10, loss tangent (tan δ _85° C), storage modulus G' and loss modulus G'' at 85°C were measured as viscoelasticity, and peel force and surface adhesion strength were measured as adhesive properties. The optical properties of haze, total light transmittance, and hue were measured, and the results are shown in Table 4.

(viscoelasticity)
The loss tangent, storage modulus, and loss modulus of the OCA sheet at 85°C were measured using a viscoelasticity measuring device "Physica MCR301" manufactured by Anton Paar. PP12 was used as the measurement plate, and the measurement conditions were as follows. Loss tangent (tan δ _85°C ), storage modulus (G'), and loss modulus at 85°C, with a strain of 0.1%, a frequency of 1 Hz, and a cell temperature of 25°C to 100°C (heating rate of 3°C/min). (G'') was recorded.

(Peeling force)
The peel force of the OCA sheet was measured by a 180° peel test in accordance with JIS K 6854-2. A test piece of length 75 mm x width 25 mm was prepared for each OCA sheet, and one side of the OCA sheet was pasted on a slide glass (alkali-free glass, product name EagleXG, manufactured by Matsunami Glass Co., Ltd.) measuring 75 mm length x 25 mm width. The pressure was maintained at 0.4 MPa for 30 minutes, and the OCA sheet and slide glass were bonded together. Next, a 125 μm thick PET sheet (“Melinex (registered trademark) S” manufactured by Teijin DuPont Films) was attached to the surface of the OCA sheet opposite to the slide glass. After that, after leaving it for 12 hours at room temperature and humidity (temperature 23 ° C., humidity 50%), the PET sheet was pulled in a 180° direction at a speed of 300 mm/min, and the OCA sheet was peeled off at the interface with the slide glass. The peeling force of the OCA sheet against a glass slide was measured.

(Surface adhesion)
A test piece with a length of 15 mm and a width of 15 mm was prepared for each OCA sheet, and measured using a "Modular Compact Rheometer MCR 302" manufactured by Anton Paar. Each test piece was pasted on the measurement plate and placed so that the test piece was located below the terminal, and the initial load value with the terminal in contact with the test piece was set to 1N. The terminal was lowered and pressed against the test piece until the load value reached 10 N, held for 10 seconds, then the terminal was raised and the maximum load value when the test piece and the terminal peeled off was measured as surface adhesion force.
<Measurement conditions>
Terminal type: SHAFT FOR DISPOSABLE MEASURING SYSTEMS D-CP/PP7
Terminal diameter: Φ12mm
Measurement plate: PP12
Terminal rising speed: 5mm/s
Measurement temperature: 85℃±0.5℃

(optical properties)
The haze and total light transmittance of the OCA sheet were measured in the same manner as in Example 1. The hue was determined by measuring L*, a*, b*, and YI in the same manner as in the evaluation of yellowing in Reference Example 1. It can be determined that there is no yellowing when a* is ±0.5 or less, b* is ±0.5 or less, and YI is 1.0 or less. When L* is 94% or more, it can be judged that transparency is high. Note that the hue measurement was performed using an OCA sheet that had not been left at high temperatures.

As shown in Table 4, all of Examples 7 to 10 have haze of 1% or less, total light transmittance of 90% or more, L* of 96% or more, and a* of ±0.5. Hereinafter, b* was ±0.5 or less, YI was 1.0 or less, and in addition to high transparency, no yellowing was observed. Further, in Examples 7 to 10, sufficient adhesive properties were confirmed. Furthermore, Examples 7 to 10 are considered to be able to effectively suppress the occurrence of delay bubbles.

(Measurement of curing time)
For the OCA sheets according to Examples 7 to 10, changes in tan δ at ₈₅ ° C. over time were measured, and the results are shown in FIG. 3. FIG. 3 is a graph showing the curing time of the OCA sheets according to Examples 7 to 10. As the thermosetting of the thermosetting polyurethane composition progresses, the amount of change in tan δ _{of 85°C} becomes smaller. As shown in FIG. 3, in Examples 7 to 10, it was confirmed that curing was completed within 2 hours.

10: Optical transparent adhesive sheet (OCA sheet)
11: Polyurethane layer 12: First surface adhesive layer 13: Second surface adhesive layer

Claims (6)

An optically transparent adhesive sheet comprising a polyurethane layer made of a cured product of a thermosetting polyurethane composition,
The thermosetting polyurethane composition contains, as a polyol component, a polyol having an olefin skeleton, and as a polyisocyanate component, a first polyisocyanate having an isocyanate group having a functional number of 3 or more, and an aliphatic and/or alicyclic compound. and a second polyisocyanate that is a group polyisocyanate. The optically transparent adhesive sheet according to claim 1, wherein the first polyisocyanate is an aliphatic polyisocyanate containing three or more isocyanate groups. The optically transparent adhesive sheet according to claim 1 or 2, wherein the polyisocyanate component further contains a modified polyisocyanate containing an alkylene oxide unit. The optically transparent pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the polyol having an olefin skeleton has a functional number of hydroxyl groups of less than 2. The optically transparent adhesive sheet according to claim 1 or 2, wherein the polyurethane layer has a thickness of 200 μm or more and 2000 μm or less. It is characterized by comprising the polyurethane layer, a first surface adhesive layer disposed on one surface of the polyurethane layer, and a second surface adhesive layer disposed on the other surface of the polyurethane layer. The optically transparent adhesive sheet according to claim 1 or 2.

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